The invention described herein relates generally to a measuring method and system. More specifically, the invention relates to a measuring method and system for measuring a gap between a rotor and a diaphragm.
For a turbine to operate efficiently, during its assembly or overhaul, it is required that its rotor be concentric with the stator. This is because between each row of the turbine blades, a packing gland or seal has to be carefully positioned to prevent steam from escaping. The packing gland consists of a labyrinth seal generally made of brass or copper and has a number of teeth that protrude from the stator housing which enter into grooves cut into the rotor shaft. The packing gland is fitted to the stator and held in place with a so-called “T” slot construction. To operate, it is essential that the rotor be concentrically disposed within the stator diaphragm, and the packing gland be concentric to the grooves in the rotor.
It is often desired to measure the concentricity of the rotor and stator with the rotor left in place. A disadvantage to this approach is that the small radial clearances between the rotor and stator diaphragm do not allow for the measurements to be taken manually due to the lack of access and constrained space. Furthermore, the small axial and radial size of the groove in the diaphragm with the minimal radial clearances between the rotor and diaphragm do not permit current known devices to be used for concentricity measurements.